Implement Trie

Linkage

Implement Trie (Prefix Tree)

Reminder

1.This is a naive implementation of Trie, which do not support the delete function, furthermore, the long string which can match multiple words is also not supported.

2.The key and value of a map must be Object, the basic type like int and char is not supported.

Code

import java.util.HashMap;

class TrieNode {
    boolean isWord;
    HashMap<Character, TrieNode> charToTrieNode;
    public TrieNode() {
        isWord = false;
        charToTrieNode = new HashMap<Character, TrieNode>();
    }
}


public class Trie {
    
    TrieNode root;
    /** Initialize your data structure here. */
    public Trie() {
        root = new TrieNode();
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        int word_len = word.length();
        TrieNode traverseNode = root;
        for (int index = 0; index < word_len; index++) {
            Character ch = word.charAt(index);
            TrieNode target = traverseNode.charToTrieNode.get(ch);
            if (target == null){
                target = new TrieNode();
                traverseNode.charToTrieNode.put(ch, target);
            }
            traverseNode = target;
        }
        traverseNode.isWord = true;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        int word_len = word.length();
        TrieNode traverseNode = root;
        for (int index = 0; index < word_len; index++) {
            Character ch = word.charAt(index);
            TrieNode target = traverseNode.charToTrieNode.get(ch);
            if (target == null){
                return false;
            }
            traverseNode = target;
        }
        
        return traverseNode.isWord;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        int word_len = prefix.length();
        TrieNode traverseNode = root;
        for (int index = 0; index < word_len; index++) {
            Character ch = prefix.charAt(index);
            TrieNode target = traverseNode.charToTrieNode.get(ch);
            if (target == null){
                return false;
            }
            traverseNode = target;
        }
        return true;
    }
}